Re: Question about classification

Alex T. posted:

> I read a couple of papers about stellar classification in 
> which classification results were reported not in terms of
> error rate, as it is usually done in classification, but 
> instead in something like : classification accuracy is 1.6
> subclasses.
>
> I don't think I fully understand this system.
>
> Does classification accuracy of 2 subclasses means that all 
> objects were classified either correctly or with neighbouring 
> class ? Not a single object was classified with a different, 
> completely randomn class ? I find it hardly reasonable.
>
> And what about accuracy of 1.6 subclasses ? Does that mean that 
> 40% percent of the objects were classified correctly and 60%
> as their neighbours ? Once again, not a single object was 
> classified absolutely randomly ?

An accuracy of 1.6 subclasses means that the spectral classification for the 
research done for that paper could be off by as much as 1.6 subclasses.  The 
classes are O, B, A, F, G, K, M, and are divided into subclasses with a 10 
step (zero to nine) decimal sub-classification.  Our sun is class G2, Sirius 
is class A1, Barnard's Star is class M5, ect.  However, it is often difficult 
to get precise sub-class classification, since it often requires detailed 
comparisons between spectra which are not at all similar in density or 
dispersion.  This is particularly true of some lower-resolution spectrographs 
which are used for faint stars in studies of things like open or globular 
clusters.  I recall the difficulties I had when doing a spectral 
classification exercise put on by my Astronomy professor using real spectra 
taken of certain stars of known spectral type.  I found it not all that easy 
to get within 2 spectral sub-classes sometimes :-) (getting the luminosity 
class right was even harder).  A 1.6 sub-class error isn't exactly horrid 
depending on the target and the instrumentation used (it means that, for 
example, a star classed as F5 could be as "early" as an F3.4 or as "late" as 
an F6.6).  Clear skies to you.
--
David W. Knisely  [EMAIL PROTECTED]
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
*    July 18-23, 2004, Merritt Reservoir     *
*      http://www.NebraskaStarParty.org      *
**********************************************